Stoker control



Mam}! 1944- G. l. HOLMES STOKER CONTROL Filed Oct. 51. 1940 1 I Rm "mm o R m 0 WA n mm A Patented Mar. 7, 1944 .STOKEB oonraor.

Giii'ord I. Holmes, Minneapolis, Minn, assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Jipplication October 31, 1940, Serial No. 363,723

7 Claims.

The present invention relates to improvements in control apparatus for fuel feeding devices, primarily stokers, wherein the device is to be controlled by a thermostat and also operated periodically under low heat requirement conditions when there are no calls for heat from the thermostat.

It is the object of my invention to provide a unitary control instrument for fuel feeding devices such as stokers, the instrument being arranged to function both as a thermostat and a timer.

Another object of my invention is to provide a heat actuated timing device for controlling a stoker, the device being responsive to space temperature as well and operable to control the stoker in accordance therewith.

Another object is to provide a control instrument for fuel feeding devices comprising a heat actuated bimetal timer and a temperature responsive element for adjusting the time in accordance with space temperature.

Figure 1 is a view ofvthe control instrument of my invention. I

Figure 2 is a diagrammatic illustration of the instrument in combination with a stoker system.

Referring to the drawing in Figure 2 Ighave shown a stoker system including my improved control instrument which is shown in diagrammatic form'in this figure. The stoker is designated by the numeral II and the control instrument by the numeral II.

The instrument H comprises a generally U- shaped bimetallic temperature responsive element l2 which is rigidly mounted as at It. Numeral I4 designates a second bimetal element responsive to heat which is mounted on the end or an arm l5 pivoted on a pivot IS. The lower end of the bimetal element I4 is attached to the free end of the bimetal element II by a link H. The instrument Ii is disposed in the space being heated by the stoker and the bimetal element i2 is relatively sensitive so as to respond to changes in the space temperature. Upon increase in space temperature the free end of the element 12 moves to the right toward a fixed stop 20, thereby moving the bimetal element It in a clockwise direction about the pivot it. The free end of the element l2 moves to the left upon decrease in space temperature.

Adjacent the bimetal element M a as electrical heating resistance. 21, the-mid point of which is connected to the bimetal element N by a wire 22. The upper end of the bimetal element It cooperateswith a pair oi iixed electrical contacts 25 which cooperates with an armature carried.

by element It as may be seen on Figure 1 so that the element ll ages with and disengages from the contacts 23 and 24 with a snap action. The details of the' control instrument Ii may be more readily ascertained by inspecting flure 1 wherein a preferred form of the instrument is shown. In Figure 1 the instrument ll comprises a base member 28 which may be fastened to a wall. The bimetal element I 2 is shown as a coiled element mounted on pivot it which is joumalled in the base ii. Attached to the pivot i6 is an adjusting arm 21 which can be moved to the right or left so as to bodily adjust the position of the element l2. Numeral 28 designates a plate attached to the lower portion of the base 26, the lower edge of the plate 28 having temperature graduations as shown. The adlusting arm 21 has an index marker 29 which cooperates with the graduations on plate 28. With the parts in the position shown on Figure l, the index 28 is opposite I. on the P e The plate 28 has an ear 30 having a bent-over portion 3| thr'ough'which extends a screw 32 which forms the stop 20 described in connection with Figure 2. The screw 32 limits movement to the right of the free end vof the element l2.

In the improved form of the instrument shown in Figure 1 the permanent magnet 25 is carried on a bracket II which is pivoted on a pivot ll and which has a downwardly extending arm 31 attached to the end of an adjusting screw 38 which extends through a bracket 38. The permanent magnet 25 cooperates with an armature 40 at the upper end of element It and by adjusting the screw 38 the bracket 35 can be moved to the right or left about its pivot, thus adjusting the position of magnet 25 with respect to armature 40. The element It also carries a contact ll at its upper end which cooperates with a contact screw 42 carried by a bracket 43. If desired, the upper end of the element It may carry an element arranged to bridge a pair of fixed contacts as shown diagrammatically on Figure 2. Whenever the armature ll is brought within the field of the magnet 25 the contact ll is snapped into engagement with contact screw 42. By adjusting the position of the magnet 25 the position at which element It will snap to the left can be adjusted. In Figure 1 the heating element 21 is-shown as being disposed in intimate thermal contact with the element I4 and if desired insulation Ila maybe placed about the heating element.

From the foregoing it is to be seen that the element I2 is operable to bodily adjust the position of element ll with respect to the contact screw 4! upon rise and fall in space temperature and that the amount which element I! can ad- Just element id to the right about pivot I8 is limited by contact screw II.

Referring now again to Figure 2, numeral 45 designates a relay for controlling the stoker It, the relay comprising a winding 46 having an armature attached to a switch blade 41, the armature moving in a direction to bring switch blade 41 into engagement with a fixed electrical contact 48 when the winding 46 i energized. Power for the control system is supplied through line conductors Ill and BI and a step -down transformer 52 having a primary winding 53 connected to line conductors 50 and by wires 54 and 55 and a secondary winding 56 having a Iewer number of turns than the primary winding.

Numeral 59 designates a manually adjustable resistance comprising a resistance element BI! and a manually slidable contact Bl.

With the parts in the position shown, the resistance 2| is connected across the secondary 55 of transformer 52 through the variable resistance E9, the circuit being as follows: mrom secondary 56 through wire 65, part of resistance tn, contact 6|, wire 68. resistance II and wire 51 back to secondary 58. The resistance 2| is of such a value that when the circuit just described is complete it produces only a negligible amount oi heat and under these circumstances the element I! slowly cools and warps to the leit until its upper end is brought into the field of magnet 25 whereupon it snaps into engagement with contacts 23 and 24, bridging these contacts. As soon as these contacts are bridged a circuit is completed for the winding I! of relay 45 as fol lows: From secondary 55 through wire It, wiuding 46, wire H, contacts 2i and 23, wire I2, and wire 61 back to secondary 56. As soon as relay ii is thus energized switch blade l'l engages contact Q8 completing a circuit for the stoker in as follows: from line conductor 50 through wire 15, stoker ll, wire Ii, switch blade 41, contact ll, and wire ll back to line conductor ll. The stoker remains energized as long as the relay 4! is energized. At the same time as the relay is energized as described above a separate circuit is completed for the lower half of resistance II, which circuit is in parallel with the circuit through relay coil 48 and which shunts the upper half of resistance 2|. This circuit is as follows: from secondary ll through wire 85, part or resistance I, contact Bl, wire I, the lower half of resistance 2|, wire 2!, element 14, contacts 24 and 23, wire 12, and wire '1 back to secondary I6. The resistance in this circuit is considerably lower than the circuit which includes all of resistance 2| and the heat produced by the lower half of resistance II is now suflicient to cause element H to warp to the right, that is, in a direction tending to move away from contacts 2! and 24. After a given period of time during which the circuit through the lower half of resistance II is complete, element It snaps away from contacts I and 24, interrupting the said circuit and also deenergizing the relay. After the circuit through the lower half of resistance II is interrupted the amount of heating is again.

substantially reduced and element I4 again slowly warps towards contacts 23 and 24. In this manner contacts 23 and 24 are periodically bridged for a short interval of time, '10). example, from two to four minutes. The characteristics of the element ll are such that after it has moved away from contacts II and 26 approximately thirty minutes elapse before it warps to the left sufliciently to rebridge contacts 23 and 24. Element I4 is relatively insensitive to space temperature inasmuch as changes in space temperature are normally not great enough to produce an appreciable amount of movement of the single bimetal strip of which element H is comprised.

The operation Just described takes place when the space temperature is at 70, the thermostat with the parts in the position shown being set for 70 as shown in Figure 1. Under these circumstances the free end of element I2 stays in substantially the same position and so the element l4 remains in substantially the same angular position on the pivot Ii. The operation as described under these circumstances, that is, periods of energization of relay of substantially two minutes and periods of deenerglzation of approximately thirty minutes are for the purpose of maintaining a fire in the furnace or boiler by the stoker II.

It the space temperature should fall below '10" causing the element I! to contract its free end moves to the left an amount corresponding to the fall of temperature, thereby moving element i4 angularly about its pivot in a counterclockwise direction. This brings the "upper end of element l4 closer to the contacts M and 24 and the result is that element ll tends to keep contacts 23 and N bridged for a longer period oi time and to leave them unbrldged for a shorter period of time depending upon the magnitude in the fall in temperature below In other words, when clement ll has a position closer to the contacts 23 and 24 it has a shorter distance to warp to the left before bridging the contacts when the relay l! is deenerglzed. Thus it is to be seen that as the space temperature decreases below 70 the operating periods of the stoker are proportionately lengthened and the intervals between operations are proportionately shortened. As the space temperature falls below 70 to a predetermined low temperature the element It will position the element l4 within the field of magnet 25 so that the contacts 23 and 1| remain continuously bridged until the space temperature again rises. The temperature value at which contacts 23 and 24 will be continuously bridged may be 65 to 67 for example, depending upon the characteristics of the bimetal elements and their relative positions of mounting.

Due to the length and sensitivity of element 12, relatively small changes in space temperature cause it to impart appreciable movements to element H.

As the space temperature rises element l2 expands, its free endmoving to the right and at a space temperature of 71 or 72", for example, its free end will engage the stop 20 preventing it from moving the element It any further angularly in a clockwise direction. When the free end of element. II engages stop it], element It is in such a position on its pivot that the operating periods of the stoker produced by element l4 and heater II are of minimum duration and the intervals between operations are of maximum length. Under these circumstances the intermittent operation of the stoker is the minimum amount required to maintain a fire in the boiler or furnace satisfactorily by the stoker. The purpose of the stop 20. is of course to prevent element I! from moving element ll so far to the right that the operating periods of the stoker are reduced in length below the minimum required. for maintenance of the fire.

As pointed out above, the element i2 is relatively sensitive, moving its free end to the right or left in response to changes in the space temperature. The element I4 is even more sensitive but responds primarily to the heater 2|. If desired insulation may be placed about the heater 2| as described in connection with Figure 1 to prevent this heat from affecting the element I2.- It is to be recognized that the element I4 and heater 2'! act primarily as atimer to provide for intermittent operating periods of the stoker. The operation of the timer is varied by the temperature responsive element l2 so as to increase the amount of operation of the stoker in accordance with the space temperature so as to maintain it at the desired value. It is to be-seen therefore that I have provided a single instrument having both a timing function for maintaining the fire and also serving as a thermostat so as to provide for sufficient operation of the stoker so as to maintain a uniform temperature under various heating requirements.

While my disclosure constitutes a preferred form of my invention, various other forms of it are comprehended as being within its scope, the principle of the invention being that of forming a single instrument in such a manner as to act as a timer as well as a thermostat for controlling a device requiring intermittent operation when there are no demands from the thermostat. My invention is to be limited therefore not in accordance with my disclosure which is representative but only in accordance with the claims appended hereto.

I claim as my invention:

1. An intermittently operable switch comprising in combination, a base having a pivot, an elongated bimetal pivoted adjacent one end thereon, a. movable contact on the other end of said bimetal, a stationary contact cooperable with said movable contact, said contacts being closed upon m vement of said bimetal in cooling direction and opened when said bimetal is heated; a magnet adjacent said contacts to render them snap acting and to establish a temperature differential between opening and closing operations; a heater for said bimetal, said heater being controlled by said contacts so as to supply a higher degree of heat to said bimetal when said contacts are closed than when they are opened; thermostat secured at one end, the second end thereof being free to move upon temperature changes, a link connecting said second end to said' bimetal whereby said thermostat may adjust the position of said bimetal to vary the operation thereof, and to a stop to prevent said thermostat from varying the position of said bimetal beyond a predetermined position.

2. In combination, a pair of temperature re'-. sponsive members mounted with relationship to each other so thatboth move in substantially the same directions on heating and cooling, one of said members being pivotally mounted and responsive substantially only to relatively great variations of heating and cooling, mechanical connecting means between saidone member and an ambient temperature responsive an active portion of said other member whereby said other member bodily positions said one member, control means operated by an active portion of said one member, and means responsive to operation of said control means for intermittently heating and cooling said one member to cause said member to intermittently operate said control means, the length of time of the intermittent operations being determined by the position of said one member.

. 3. In combination, a pair of temperature responsive members mounted with relationship to each other so that both move in substantially the same directions on heating and cooling, one of said members being pivotally 'mounted and responsive substantially only to relatively great variations of heating and cooling, mechanical connecting means between said one member and an active portion of said other member whereby said ,other member bodily positions said one member, control means operated by an active portion of said one member, means responsive to operation of said control means for intermittently heating and cooling said one member to cause said member to intermittently operate said control means, the length of time .of the intermittent operations being determined by the position of said one member, and means for limiting the amount that said one member may be positioned to prevent said operations from decreasing below a predetermined minimum length of time.

4. In combination, a thermostat comprising a first temperature responsive member, control means operated by an active portion thereof, heating means for said first temperature responsive member controlled by said control means, said heating means being wholly energized when said control means is in an active position and partially energized when said control means is in an inactive position, said heating means being adapted to cause said first temperature responsive member to move through a predetermined range of movement; a second temperature responsive member responsive to ambient temperature variations and movable through a predetermined range of movement in response thereto, and mechanical connecting means between said temperature responsive members whereby said second temperature responsive member in different places of its range of movement causes said first temperature responsive member to operate in different portions of its range of movement to thereby vary the control characteristics of said thermostat 5. In combination, a thermostat comprising a first temperature responsive member; control means operated by an active portion thereof, heating meansfor said first temperature responsive member controlled by said control means, said heating means being wholly energized when said controlmeans is in an active position and partially energized when said control 'means is in an inactive position, said heating means being adapted to cause said first temperature responsive member to move through a predetermined range of movement; a second temperature responsive member responsive to ambient temperature variations and movable through a predetermined range of movement'inresponse thereto, mechanical connecting means between said temperature responsive members whereby said second temperature responsive member in different places of its range of movement causes said first temperature responsive member to operate in different portions of its range of movement to thereby vary the control characteristics of said thermostat, and means for limiting the movement 0! said second temperature responsive member to prevent said first temperature responsive member from being positioned beyond a predetermined range 01' movement.

6. In a temperature control device, in combination, a thermal timer including switchinl means and a temperature responsive element deformable on changes in temperature in a first direction to actuate said switching means, means responsive to changes in space temperature and thermally insulated from said thermal timer for positioning said temperature responsive element bodily to actuate said switching means or to render said switching means MIOBMVE, and means for" limiting the bodily" 9v merit of said temperature responsive eleme: My said space temperature responsive moans a dime om tending to render said switehilig means ineiiec tlve, whereby said temperature responsive assaero ment is capable of actuating said switching means regardless of space temperature.

7. In apparatus of the character described, in combination, a stoker, control apparatus for the stoker comprising a thermal timer including electrical switching means for causing operation of said stoke! when actuated and a temperature responsive element deformable on changes in temperature in a first direction to actuate said switching means, means responsive to the temperature of the space being heated and thermally insulated from said temperature responsive element for positioning said temperature responsive Witching means, 

